The Phycodnaviridae virus Family consists of six known Genera, all of which infect algae*. These algal hosts have some pretty interesting stories on their own.
For instance, Phaeophycaea (also known as brown algae) is a Class within Eukaryotes that is made up of sea weeds. Many people assume that these organisms are more closely related to plants – but really they are as related to plants as are the animals. The NCBI Taxonomy browser shows what are probably two different Phaeoviruses, Ectocarpus siliculosus virus and Feldmannia irregularis virus – both named for the species of seaweed they were isolated from. That even seaweeds have their own viruses illustrates my favorite statement “successful systems attract parasites”, which to a virologist translates to: all species have viruses. Another interesting characteristic of Phaeoviruses? They only transmit by infecting their gametes (sperm and egg). Yes, seaweeds do that too.
Coccolithophores and Prymnesiophytes appear to be very closely related groups housed in the Haptophyte Division (Division in Botany is the same as Phylum everywhere else). These photosynthetic single celled creatures take in carbon dioxide from the air to build themselves, including the most beautiful armored plates made of calcium carbonate. They occasionally divide like crazy and form giant blooms. The viruses that infect them then end these giant parties, destroy these beautiful cells and send their beautiful armor to the bottom of the ocean. Being made of calcium carbonate, those shells** take lots and lots of carbon (which came from carbon dioxide in the air) with them and thus this virus:host system plays a major role in global carbon cycling. And the white cliffs of Dover. There is a wonderful Radiolab episode covering this.
Then there is Chlorella – the whole reason that I am interested in Phycodnaviruses in the first place. I came across Chlorella and their viruses not because of Chlorella, or their viruses. I was transitioning from full time research on animal viruses to teaching, and while I was sick of laboratory research as a way to make money to raise a family, I was most definitely NOT sick of laboratory research as a way of discovering new questions to ask. One of the best tools a virologist can have is called a plaque assay – basically a way of counting how many viruses there are in a given sample. This might not sound exciting, but it allows you to ask a whole bunch of questions, really basic ones that are very satisfying. I am not sure how I came across it, but during this transition into teaching I found a published plaque assay protocol for a virus that infects a unicellular green algae named Chlorella. The protocol struck me as something that students could do in a classroom laboratory and that is exactly what I am trying to eventually get to.
Chlorella is a genus of unicellular algae that is widely found in fresh water. “Widely” is an important word there because in my plan, I am going to have students looking for viruses that infect them from local ponds, lakes and rivers. I used to hate this kind of approach – technique driven questions – as opposed to asking the questions first and then finding the right technique to answer them. I am so limited in resources however, that this is the only practical way to make progress. The first goal is to get my students counting viruses in our teaching labs. Answering questions is actually secondary to that, but I think there are some fascinating questions that could be addressed if we can get it going.
Chlorella also have a trick up their sleeve: they often are found as endosymbionts inside of Ciliates (such as Paramecium), which they undoubtedly supply with sugars from photosynthesis. This is a very new (and strange!) field to me, but a recent review certainly suggests that there are lots of unanswered questions about endosymbiosis in Ciliates.
The particular virus that this plaque assay used is Paramecium Bursaria Chlorella Virus -1 (PBCV-1) and, like all of the Phycodnaviruses, its somewhat odd (more later).
* – The word “algae” really doesn’t help us much here – not all species called algae are close cousins but for now that will do.
** – technically called “coccoliths”
W. H. Wilson, J. L. Van Etten, and M. J. Allen. (2009). The Phycodnaviridaea: the story of how tiny giants rule the world. Curr Top Microbiol Immunol. 2009; 328: 1–42.